# JavaScript: Replace the first digit in a string (should contains at least digit) with \$ character

## JavaScript Basic: Exercise-136 with Solution

Write a JavaScript program to replace the first digit in a string (should have at least one digit) with the \$ character.

Pictorial Presentation: Sample Solution:

HTML Code:

``````<!DOCTYPE html>
<html>
<meta charset="utf-8">
<meta name="viewport" content="width=device-width">
<title>Replace the first digit in a string (should contains at least digit) with \$ character</title>
<body>

</body>
</html>
```
```

JavaScript Code:

``````function replace_first_digit(input_str) {

return input_str.replace(/[0-9]/, '\$');
}
console.log(replace_first_digit("abc1dabc"));
console.log(replace_first_digit("p3ython"));
console.log(replace_first_digit("ab1cabc"));
``````

Sample Output:

```abc\$dabc
p\$ython
ab\$cabc
```

Flowchart: ES6 Version:

``````function replace_first_digit(input_str) {

return input_str.replace(/[0-9]/, '\$');
}
console.log(replace_first_digit("abc1dabc"));
console.log(replace_first_digit("p3ython"));
console.log(replace_first_digit("ab1cabc"));
``````

Live Demo:

See the Pen javascript-basic-exercise-136 by w3resource (@w3resource) on CodePen.

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## JavaScript: Tips of the Day

Reduce method

```[1, 2, 3, 4].reduce((x, y) => console.log(x, y));
```

The first argument that the reduce method receives is the accumulator, x in this case. The second argument is the current value, y. With the reduce method, we execute a callback function on every element in the array, which could ultimately result in one single value.
In this example, we are not returning any values, we are simply logging the values of the accumulator and the current value.
The value of the accumulator is equal to the previously returned value of the callback function. If you don't pass the optional initialValue argument to the reduce method, the accumulator is equal to the first element on the first call.
On the first call, the accumulator (x) is 1, and the current value (y) is 2. We don't return from the callback function, we log the accumulator and current value: 1 and 2 get logged.
If you don't return a value from a function, it returns undefined. On the next call, the accumulator is undefined, and the current value is 3. undefined and 3 get logged.
On the fourth call, we again don't return from the callback function. The accumulator is again undefined, and the current value is 4. undefined and 4 get logged.

Ref: https://bit.ly/323Y0P6

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